Reference for Bava Metzia 4:12
הַתַּגָּר נוֹטֵל מֵחָמֵשׁ גְּרָנוֹת וְנוֹתֵן לְתוֹךְ מְגוּרָה אַחַת. מֵחָמֵשׁ גִּתּוֹת, וְנוֹתֵן לְתוֹךְ פִּטָּם אֶחָד. וּבִלְבַד שֶׁלֹּא יְהֵא מִתְכַּוֵּן לְעָרֵב. רַבִּי יְהוּדָה אוֹמֵר, לֹא יְחַלֵּק הַחֶנְוָנִי קְלָיוֹת וֶאֱגוֹזִין לַתִּינוֹקוֹת, מִפְּנֵי שֶׁהוּא מַרְגִּילָן לָבֹא אֶצְלוֹ. וַחֲכָמִים מַתִּירִין. וְלֹא יִפְחֹת אֶת הַשָּׁעַר. וַחֲכָמִים אוֹמְרִים, זָכוּר לָטוֹב. לֹא יָבֹר אֶת הַגְּרִיסִין, דִּבְרֵי אַבָּא שָׁאוּל. וַחֲכָמִים מַתִּירִין. וּמוֹדִים שֶׁלֹּא יָבֹר מֵעַל פִּי מְגוּרָה, שֶׁאֵינוֹ אֶלָּא כְגוֹנֵב אֶת הָעָיִן. אֵין מְפַרְכְּסִין לֹא אֶת הָאָדָם וְלֹא אֶת הַבְּהֵמָה וְלֹא אֶת הַכֵּלִים:
A merchant may take (produce) from five threshing floors and place it into one storage bin. [For all know that it was not grown in his fields and that he bought it from many people; and they buy it from him with this understanding. (It was the custom of merchants to buy (produce) from field owners at threshing time and to place it in their bins)]. (He may take wine) from five wine vats and place it in one cask, so long as he does not contrive to mix them, [letting it out that he bought most of it from a "prime" source, and mixing it (with wine) from a different place, his neighbors thinking that it is all from the same source.] R. Yehudah says: "A shopkeeper should not hand out parched ears and nuts to children because he thereby accustoms them to come to him. The sages permit it. And he may not sell below the market price [because he thereby accustoms people to come to him and constricts his neighbor's livelihood.] The sages say: "May he be remembered for the good!" [For this brings the price down. And this is the halachah.] One may not sift (the chaff of) grisin (beans split in a mill, one into two. For their improved appearance enables him to raise the price beyond the worth of the chaff removal.] These are the words of Abba Shaul. And the sages permit it. [For the buyer can evaluate the cost of chaff removal by comparing them with others. And it is worth his while to pay more for these sifted ones to spare himself the trouble (of sifting). The halachah is in accordance with the sages.] And they concur that he should not do so (only) on the surface of the container [to enhance their appearance, without having sifted the chaff below], for he is only an "eye-stealer" [with this surface sifting.] One may "touch up" neither a man [a Canaanite bondsman awaiting sale], a beast, nor vessels.